1. Field of the Invention
The present invention relates to a fuel cell stack.
2. Description of the Related Art
In a conventional fuel cell stack, fuel cells are stacked in a horizontal direction, and a cathode gas inlet manifold is disposed in an upper portion of one of the ends of the fuel cell stack. Also, a buffer portion is provided on a cathode separator which is a component of a fuel cell stack so that the width of a passage increases from the cathode gas inlet manifold to a gas passage. In addition, a cathode gas outlet manifold is disposed in a lower portion of the other end of the fuel cell stack. Further, a buffer portion is provided on the cathode separator so that the width of the passage increases from the gas passage to the cathode gas outlet manifold.
As a result, a cathode gas smoothly flows from the cathode gas inlet manifold to the cathode gas outlet manifold. See, for example, Japanese Unexamined Patent Application Publication No. 2006-236612. However, the above-mentioned conventional fuel cell stack has a problem in that when condensed water is produced in the fuel cell stack after power generation is stopped, the condensed water collects in the gas passage of the separator, potentially blocking gas flow from the cathode into the cathode gas outlet manifold. This problem is particularly significant when the fuel cell stack is operating in ambient temperatures below the freezing point of water, such that the condensed water collected in the gas passage of the separator can freeze.